Refining liquid hydrocarbon distillates



Patented 3, 1939' PATENT orrlca REFINING LIQUID YDROOARBON I DISTILLATES Waldo (i. Ault and Carroll A. Hochwalt. Dayton.

Ohio, assignors to Monsanto Chemical Company. St. Louis. Mo.. a corporation of Delaware No Ilrawiuga- Application March 8. 1986. Serial No. 66.895

10 Claims.

This invention relates to the refining of petroleum distillates for motor fuel purposes which are rich in impurities that impart, colorand odor, or are productive of gum. In addition.

5 the invention contemplates a treatment whereby the antiknock value of the fuel is increased and the susceptibility to tetra ethyl lead is improved.

The petroleum fractionswhich may be treated according to the present invention are generally made by cracking relatively higher boiling petroleum products. However, they may also be produced by polymerizing lower boiling products. In either case the raw material having the desired boiling range for motor fuelpurposes may be malodorous, off color, rich in gum forming constituents, and may frequently contain sulfur in objectionable amounts.

Various methods are now used to refine this. so called, raw gasoline to render it suitable for motor fuel purposes. In most instances several successive treatments are necessary in order that a product having the desired properties is ultimately obtained. One common procedure for removing the sulfur and gum forming constituents consists in washing the raw gasoline with sulfuric acid, subsequently with water, and thereafter with alkali to remove residual acidity. The product is then redistilled.

An alternative procedure consists in contacting the raw gasoline with active clay, whereby the gum forming constituents are partially separated. It is generally necessary to follow the clay treatmentwith a doctor treatment, which is calculated to remove objectionable odors, cs- 35 pecially those attributable to the presence of sulfur impurities. necessary in the case of'acid treated gasoline. With either method of treatment gum inhibitors are commonly added to the gasoline, especially 40 if the gasoline is apt to be stored for a considerable riod of time beforeuse.

Present day practices share many objectionable features. Thus, for example, the sulfuric acid treatment is not selective. In other words, 45 it not only combines with the gum forming constituents, but also with the desirable olefinic components of a raw gasoline, thereby reducing the yield of gasoline and impairing the antiknock quality of the product. A reduction in '60 the amount of sulfuric acid employed to reduce the loss'of. desirable motor fuel constituentsis possible only to a limited extent inasmuch as ato of the gasoline is desired. Because it is not Not infrequently this is also possible to improve gasoline with regard to the presence of sulfur and gum forming constituents without materially reducing the yield and antiknock properties of the fuel, refiners indulge in a compromise between gum and sulfur impurities on the one hand and cost of refining reagents and sacrifice in yield on the other. Thus. for example, a treatment with sulfuric acid may lower the antilmoclc value of a fuel 5 to 15 points 1: a substantially gum free and low sulfur product is desired. At the same time ten per cent or more of the fuel may be lost as sludge.

The clay treatment avoids certain oblectionable features of the sulfuric acid treatment, but has no effect whatever on sulfur. Furthermore, the clay treatment does not eliminate the gum forming constituents entirely, but rather eliminates only part of these to give temporary stability and necessitates the use of so-called gum inhibitors in the finished gasoline product to attain relatively permanent stability.

Whether one employs the clay or acid treatments. it is generally necessary, in order to obtain a gasoline product having the required color I stability and freedom from odor, to subject it to a sweetening treatment. This treatment requires the use of additional chemical reagents and necessitates several additional steps in the refining operation. a

In the usual sweetening reaction. the morcaptans are transformed quantitatively to disulndes. This is usually accomplished with the aid of a source of oxygen. The presence of small quantitles of disulfides contributes materially to poor color stability, poor susceptibility to the effect of tetra ethyl lead, poor susceptibility to gum inhibitors. and to an actual loss in octane number. In addition, the presence of free sulfur, which is normally required in excess to assure complete conversion of the mercaptidel to diare attained:

1. Practically complete and selective removal lb Original Treated Gum value cu. dish" 599 2 Sulfur content percent 17 09 Bromine unslgtura on numbe 64. 3 616g 0 t no num r Cgl r Yellow Water white Approximate yield percent 98 4. No loss in the desired olefin or aromatic 0011- stituents. I

5. Substantial reduction of sulfur impurities.

6. Improved susceptibility to, and permanence of tetra ethyl lead treatment.

7. Improved color stability.

8. Nearly total elimination of treating reagent and processing operation costs.

9. Recovery of gum and sulfur components in a non-corrosive utilizable form.

10. General applicability of refining method to widely varying raw gasolines whereby a product having a, high induction period is readily and conveniently obtained.

According to the present invention, raw gasoline is subjected, while in liquid phase and at elevated temperatures, to the action of phosphoric acid, whereby the gum forming constituents and a substantial portion of the sulfur containing impurities are converted into relatively higher boiling compositions that are thereby effectively and completely rendered separable from the desired gasoline product bydistillation. The temperature of treatment, time and conditions of contact between theacid and the gasoline, and theconcentration of the acid are so adjusted with re- .exception of the removal of hydrogen sulfide,

which is effected completely either by a water or alkaline wash. I

The following comparative analyses of a gasoline before and after treatment are typical of the results obtainable by practicing our invention:

We are aware that it has been proposed heretofore to treat various hydrocarbons with mixtures of phosphoric acid and sulfuric acid. However,

I we have found that under the conditions of our process in its preferred form sulfuric acid is rapidly decomposed. We are also aware that it has been proposed heretofore to pass hydrocarbon vapors in admixture with steam over a carrier sprayed with phosphoric acid (U. S. P. 1,709,315)

- However, such process is ineffective or only partially effective at best and must be supplemented by additional chemical treatments, such as, for example, a hypochlorite treatment. Furthermore, the various acids ofphosphorus have been considered ineffective in and of themselves for the purpose of refining raw gasoline (U. S. P. 1,914,-

953) and to the best of our knowledge the use of these acids has met with no commercial success in this field.

In contrast with the foregoing, the following examples illustrate specific procedures for applying the principles of our invention:

Example I Approximately 1.00 c. c. of a cut of a commercial cracked gasoline boiling at l30-200 C. were placed in a 1-liter, 3-necked flask equipped with an efiicient stirrer and reflux condenser, to which there was added ten per cent by weight of ortho phosphoric acid (HsPO-i) The mixture was stirred rapidly and heated at reflux temperature for about 45 minutes. At the end of this period the mixture was cooled, allowed to stratify and the gasoline layer was then decanted from the acid. The gasoline was then washed with a dilute aqueous alkali after which the water free gasoline layer was redistilled.

The following characteristics, comparing the refined gasoline with the original material, illustrate the value of this treatment:

Original Treated 187. 0 4. 5 Bromine value 50.0 45. 8 Sulfur .per cent. 0. '75 17 Oxygen bomb stability hours 1 5% Example II Approximately five hundred c. c. of a commercialcracked gasoline were introduced into a steel bomb along with 40 grams of. a. mixture of phosphoric acids prepared by dissolving 4 or 5 grams- QfPgOs in 35 grams of 1 00% ortho phosphoric acid. Such a mixture probably contains orthopyroand possibly some meta-phosphoric acids. After closing the bomb, heat was applied and the stirring device started to promote contact between the catalyst and the gasoline. The heating was continued one-half hour, at a temperature of 150 0., a pressure of about 125 pounds per 511.1 in. being attained.

At the end of one hour the mixture was cooled I rapidly and the contents of the bomb removed and allowed to stratify. The gasoline layer was decanted and redistilled, without fractionation and cut at about 200 C. The resulting product was practically free of gum, water white and very stable.

.Example III I Substitute for the acid catalyst of Example II an equal weight of 100% Example IV Substitute for the acid catalyst of Example II an equal weight of 100% phosphoric acid (H3PO4) in which there is dispersed or dissolved one-half of one per cent of a mixture of equal parts by weight of copper and cadmium hydroxides; otherwise proceed. as in Example 11. The product which was refined in this manner was found to be practically free of gum, was of improved octane number and had an appreciably.

reduced sulfur content.

In our co-pending application filed of even date, we have shown that if a substantially waterform composition were obtained which were at a temperature of approximately HIP-185 C. These vapors were introduced through a quarter .inch tube-into phosphoric acid of approximately concentration and allowed to bubble upwardly through about 6 to 10 inches of the acid which-was maintained at approximately (P- C. by an oil bath'that surrounded all except a small portion of the upper extremity of the catalyst containing vessel. Buflicient reflux was thus afforded in relation to the temperature, acid concentration, etc. to produce a clean separation of gum forming constituents and substantial separation of sulfur containing constituents in the form of a relatively high boiling polymer. which polymer was all retained in the catalyst containing vessel and in intimate admixture with'the catalyst. This intimate mixture of polymer and catalyst was found to be at least as good a scrubbing medium for the purpose of our invention as the'acid itself.

Following condensation of the scrubbed vapors,

a light aqueous alkali wash was used to remove,

the traces of hydrogen sulflde. The following were the characteristics of the original and the treated gasoline:

Original Treated al illi ms 1 0.0. Y m (flLdllh... ass s Sulfur content (lam method)...per t.. 0.16 0.07 Bromine unsaturat n numberlbromi ebromste reagent) 0t. 0 ill. I Octane number I ti on t s 21.1 (lclorn n Water white Approximate yield percent. v 09 The oily polymer was formed in the phosphoric acid to the extent of about 1% of the weight of the gasoline treated. This polymer upon subsequent distillation at atmospheric pressure possesed a boiling range. of 240-380' 6.: only a small undistilled residue remained. During operation of the process the polymer was disseminated throughout the acid in the form of tiny globules by the flow of gasoline vapors through the liquid mixture. Upon stopping.the flow of vapors throughthe catalyst the liquid polymer rose rapidly to the surfaoe'of the acid and was thereupon separated from the acid by decontation in a substantially acid free condition. The acid layer was thus recovered practically quantitatively and in exoellenficondition for repeated In our co-pending application. filed of. even date, we have likewise shown that it a treated gasoline containing the polymer is distilled in the presence of water the polymerised products, which-are otherwise separable from the desired gasoline product by simple distillation, are chrried along with the.gasoline vapors and steam into the condensate. It was shown, however.

,that if the gasoline is first decanted to remove the. water 'and' subsequently distilled, a clean separation of the gum producing polymer from acids. In the case of the acids of lower state of the stable gum free gasoline' fraction was obtained. We have also shown that if the gasoline vapors containing the steam and the polymer are treated whereby the water is removed, the polymer can be separated by fractionation or partial condensation, and as an alternative that the gum forming constitutents present in the vapors can be removed, even in the presence of the steam by scrubbing with liquid phosphoric acid, or other suitable scrubbing media, especially high boiling materials which are liquid yet substantially nonvolatile under the conditions of treatment such as lubricating oil, paraffin, and the like.

By way of illustration, a commercial cracked gasoline was treated by flash distilling the raw gasoline at a rateof 200-300 c. c. per hour in such a manner that throughout the run vapors of substantially uniform composition were obtained which were at a-temperature of approximately NIP- C. I Along with the gasoline vapors steam was introduced in a quantity euivalent to about 2 or 3 per cent of the gasoline being treated. These vapors were introduced through a quarter inch tube into phosphoric acid of approximately 85% concentration and allowed to bubble upwardly through about 6 to 10 inches of the acid which was maintained at approxi-- mately l70-180 C, by an oil bath that surrounded all except a small portion of the upper extremity of the catalyst containins vessel.

If the gasoline vapors. are condensed one obtains a product which is rich in gum forming constitutents. However. as stated above, if the water in the condensate is decanted and the gasoline layer is redistilled. the polymer is thereby conveniently and completely separated and a product, which is practically gum free and is of substantially reduced suliurcontent, is obtained. Instead of-condensing the vapors and subsequently redistilling the gasoline layer, one may pass the vapors through a medium capable of removing the water such for example, lime (CaO), or alternatively, one may scrub the vapors with scrubbing media, which hold back the gum. Suitable media include phosphoric acid, parafiln or hydrocarbdn oils. which have an affinity or solvent action for the polymer in the vapor and which are liquid and substantially non-volatile under the conditions of the scrubbing operation.

While ortho phosphoric acid is admirably suit-- ed for the purpose of our present process, in that it not only effects substantially complete conversion of the gum forming constituents into separable form, but in addition attains the other desirable obiectives of the present invention, nevertheless other catalytic compositions may be subbe employed, or alternatively a mixture of the meta, pyro and ortho phosphoric acids. In lieu -of phosphoric acids the corresponding phosphorone, and hypophosphorous acids may be substituted in whole or in part for the phosphoric oxidation there is evidence that the materials react, at least in part, to form the more stable phosphoric acid with attending formation of phosphine. 1

In addition to the oxygen acids of phosphorous.

one may use the acid salts to replace the free acid in whole or in part. 7 Similarly one-may substitute the alkyl or aryl acid esters, which evidently likewise undergo some chemical change in thecourse of their use, but as in the other instances, the II reaction. products are themselves catalytically active.

While from the standpoint of availability the oxygen acids of phosphorus and their derivatives are especially suitable, we may use other known non-reducible acids of phosphorus, such, for example as the sulfur containing acids of phosphorus or the sulfur and oxygen containing acids of phosphorus, as for example, the thiophosphoric acid HaPSOa, or dithiophosphoric acid.

The catalyst may be made in various ways, for example, one may use ordinary phosphoric acid syrup of commerce, which is approximately per cent H3PO4. However, if desired, one may use per cent H3PO4 by adding sumcient P205 to the phosphoric acid syrup of commerce to combine with the fresh water. An excess of P205 may be added to the phosphoric acid syrup over and above that required to react with all of the water to form 100 per cent HaPOl, in which case one obtains a mixture of the pyro and ortho phos phoric acid, or depending upon the amount of P205 added, a mixtureof all three of the phosphoric acids. Instead of adding P205 to the commercial phosphoric acid, one may add P203.

The composition of the starting catalytic material may be varied considerably inasmuch as it undergoes somechange with use in attaining an equilibrium. This is particularly true with respect to the water content of the catalytic composition,

While we prefer to use a catalytic composition ,which is immiscible with the polymer by stratification and decantaticn or draining, his to be understood that the catalyst can be present asa solid,

. in which case it may be used as such or suspended or dispersed in the polymer or some other fluid inert vehiclem A further modification of the cataIytic composition consists in the use of catalytically active salts either alone or in admixture with the free acids which salts exert desirable catalytic influences. Such effect is produced by the addition of salts of catalytically active metals, such as copper, nickel, cadmium, zinc, cobalt, chromium, iron and other heavy metals. For this purpose one may add a small amount of a salt as for example a phosphate, of the metal to the fluid acid catalyst or one may incorporate a small amount of oxide directly with the acid, in which case the oxide probably combines with the acid to form the salt in situ. The effect of the addition of the salts is to reduce the temperature of the reaction or the required time of contact, and to some extent in changing the nature of the hydrocarbons being treated as to improve substantially the antiknock value, while at the same time eliminating gum forming constituents, sulfur and the like. The amount of the catalytically active metal or salt which is used may vary from the fraction of a per cent up to several per cent.

In this specification we referred to the undesirable constituents of the gasoline, which are separated by our process, as gum forming constituents; in the catalyzed form these constituents have been referred to sometimes as polymers. While we believed that the material separated, is in fact the'gum producing fraction of the raw gasoline in the form of a polymer that includes sulfur impurities of the raw gasoline,

probably in the form of a reaction product of some sort or other, it is to be understood that our invention is not limited by any theory to explain the effects. Similarly, while we refer to the process as a catalytic process (in view of the fact that there appears to be no perceptible consumption in the acid reacting phosphorus reagent), it is to be understood that we arenot in a position at this time to classify the nature of the reactions which contribute to the success of our process.

Under the preferred conditions of operation the Engler distillation characteristics of the raw gasoline are not changed substantially. Nevertheless, in view of the relatively wide range of temperature condition which can be used without departing from the scope of our invention, as well as the fact that chemical changes additional to those incident to gum removal may take place, especially as the reaction temperature approaches cracking temperatures, we do not-limit ourselves to a product whose Engler distilling characteristics are exactly reproduced in thermal product.

In general, we prefer to operatebelow cracking temperatures, that is, temperatures such as are commonly used if) the art today in converting relatively high boiling hydrocarbons to those of gasoline boiling range. One of the distinct advantages of our process resides in the. fact that widely varying raw cracked gasoline distillates may be treated without necessitating extensive changes in the treating conditions, such as -temperature, time of contact, etc. Nevertheless, under some conditions successive treatments such as might be had by subjecting the gasoline to two catalytic operations in series or by recycling the stock in a batch-wise manner, fall within the perview of our invention.

We have found it convenient in preparing the catalyst to dissolve or su pend P305 in phosphoric acid of commerce whic acid usually contains about 15% water. By adding sufllcient P205 the ortho phosphoric acid is probably converted to pyro phosphoric acid and perhaps to meta phosphoric acid. If desiredone can add sumc'ient P205 to retain a portion thereof in unreacted form. As a rule there is sufficient water in the gasoline to combine with such P205 especially after a long period of treatment, even thoug the amount of water dissolved in a decanted ra gasoline is very small. One of the advantages of the present invention resides in the fact that the reacted P205 product is itself an excellent treatment, the heating being continued until the gum forming constituents are converted to relatively high boiling products that can be separated from the liquid hydrocarbons by distillation, separating the liquid hydrocarbons fromthe acid of phosphorus and subsequently subjecting the separated hydrocarbons to fractional distillation to remove the high boiling products. 1

2. The method as defined in claim 1 and further characterized in that the acid of phosphorus is a phosphoric-acid.

3. The method as defined in claim 1 and fur-. ther characterized in that the acidof phosphorus issupplemented by a salt of a catalytically active metal selected from the group: copper, nickel, cadmium, zinc, cobalt, chromium and iron.

4;. The method as de ed in claim 1 and further characterized in hat the separated acid of phosphorus is recycled.

5. The method as defined in claim 1 and further characterized in that the heating treatment is continuous and the acid of phosphorus is recycled. I

6. The method as defined in. claim 1 and further characterized in that the reaction is eflected at super-atmospheric pressure. 7. A process treating hydrocarbon oil comprising heating the same in contact with an acid of phosphorus below cracking temperature at a pressure such that the oil is maintained substantially in the liquid state, separating the liquid hydrocarbon; from the acid' of phosphorus and subjecting the separatedhydrocarbon to. fractional distillation.

8. A process of treatinghydrocarbon oil comprising heating the same in contact with a catalyst comprising an acid of phosphorus and a salt of a catalyticaliy active metal of the group consisting of copper, nickel. cadmium. zinc. cobalt, chromium and iron below cracking temperature at a pressure such that the oil is maintained substantially in theliquld state, separating the liquid hydrocarbon irom the acid of phosphorus and subjecting the. separated hydrocarbon to fractional distillation.

9. A process of treating cracked hydrocarbons of gasoline motor fuel boiling range, comprising heating the cracked hydrocarbons in contact with a phosphoric acid below cracking temperatureand at a pressure such that the cracked hydrocarbons are maintained substantially in the liquid state, separating the liquid hydrocarbons from the phosphoric acid and subjecting the separated cracked hydrocarbons to fractionaldistlilation.

10. The method-oi treating liquid cracked hydrocarbons of gasoline motor fuel boiling range which are rich in gum. forming constituents to produce a product which is substantially free of gum and is otherwise of excellent motor iuel quality, comprising heating the liquid hydrocarbons below cracking temperature while maintaining the liquid phase in the presence of an acid of phosphorus, which acid is substantially non-volatile at the temperature of the treatment, the heating'b eing continued until the gum forming constituents are converted to relatively high boiling products that can be separated from the liquid hydrocarbons by distillation, separating, the liquid hydrocarbons from the acid of phosphorus arid subsequently subjecting the separated hydrocarbons to fractional distillation to remove the high boiling products.

WALDO C. AULT.

CARROIL A. HOCHWALT. 

